1. Field of the Invention
The present invention relates to a method for producing an integrally formed cylindrical member, having spline grooves on its inner surface, from a disc-shaped material by cold forming and to the cylindrical member produced by the method.
2. Description of the Related Art
A conventional front cover of a torque converter has a spline-grooved drum, that is attached to the front cover by welding or the like, for mounting clutch plates of a lockup clutch, as described in, for example, Japanese Patent Application Laid-Open No. HEI 9-317848.
However, the above-described construction necessitates welding the front cover to the drum. Therefore, this construction is labor intensive, creates a possibility of metal fines remaining inside, and requires a high level of quality control. Furthermore, there are also the drawbacks of an increased number of component parts and an increased cost.
To solve these problems, U.S. Pat. No. 5,718,311, for example, proposes a method for forming a front cover portion together with spline grooves by cold forming. However, simple employment of cold forming results in a considerable reduction in the wall thickness of an outer cylindrical portion of the front cover in which the spline grooves are formed. Since the outer cylinder portion of a torque converter receives high hydraulic pressures due to centrifugal forces caused by rotation of the turbine, the outer cylindrical portion requires a wall thickness that can withstand such high hydraulic pressures.
One measure for securing such a wall thickness is to merely increase the wall thickness of the entire front cover. However, by this approach even the central portion of the front cover, that does not need to be resistant to such high pressures, is formed with a thick wall. Thus, there are problems of a weight increase of the front cover and therefore a weight increase of the entire torque converter.
Accordingly, it is an object of the invention to provide a method of producing a spline-grooved cylindrical member that is capable of provision of a proper wall thickness for an outer cylindrical portion of the cylinder member in a process of cold forming, and a cylindrical member having spline grooves.
One aspect of the invention provides a method for producing a cylindrical member, having at least one spline groove on the inner surface of its outer cylindrical portion, from a disc-shaped blank material. In the method, a thick wall portion, whose thickness is greater than the plate thickness of the blank, is formed in the outer cylindrical portion through plastic deformation of the outer peripheral portion of the blank material by pressing with a roller. The outer peripheral portion of the cylindrical member is then formed integrally with the spline groove portion by pressing the thick wall portion of the blank against a mandrel having spline grooves corresponding to the spline grooves to be formed in the outer peripheral portion, through use of a forming roller.
The direction of the force applied to the blank, in pressing the outer peripheral portion against the mandrel by the thickness-increasing roller, is not critical so long as the outer peripheral portion of the blank material is thickened. For example, the thickness-increasing roller may be pressed against the outer peripheral portion in the direction indicated by an arrow E in FIG. 3. Movement of the thickness-increasing roller may also be in the direction indicated by arrows C, D, in accordance with the configuration of the thick wall portion, the dimensions of the thickness-increasing roller, etc. Optionally, the thickness-increasing roller may be pressed in a direction obliquely against the blank, i.e. in a direction intermediate the direction indicated by the arrow E and the direction indicated by the arrow C or D.
In the above-described method, the outer cylindrical portion is pressed to provide a wall thickness that is greater than the wall thickness of the blank, using the thickness-increasing roller, before cold forming of the outer cylindrical portion using the forming roller. Therefore, although in the conventional method it is necessary to use a blank of an overall thickness equal to the desired wall thickness of the outer cylindrical portion, the method of the present invention is able to form a thick-walled cylindrical member capable of withstanding high pressure acting on its outer cylindrical portion without limitation to the wall thickness of the blank. Therefore, even after forming the spline groove, a wall thickness at the bottom of the groove greater than the wall thickness of the blank can be realized. Hence, a cylindrical member capable of withstanding high pressures acting in its outer cylindrical portion can be produced from a plate having a wall thickness this is less than the final wall thickness of the outer cylindrical portion. Therefore, a useless thickness of material in other portions is avoided, and a cylindrical member having an optimal configuration can be produced. Furthermore, since the outer cylindrical portion does not need to be reinforced by a separate member, there is no need for labor-intensive welding or the like, thereby eliminating the problem of sputters of welding material, and the like.
In the above-described method, the mandrel used to form the thickened wall portion through use of the thickness-increasing roller and the mandrel used for formation of the spline groove in cooperation with the forming roller may be one and the same mandrel.
If the thickness-increasing step utilizing the thickness-increasing roller and the spline groove forming step utilizing the forming roller are performed using a single mandrel, the operation of replacing the mandrel with different mandrel for each step of processing the blank material is omitted, thereby simplifying the production process.
In another aspect the invention provides a cylindrical member with a spline groove produced by the method of the invention described above.
Therefore, since the cylindrical member having a high-pressure-resistant thick-wall outer cylindrical portion and a thin-wall portion of a thickness corresponding to the thickness of the blank is produced from a single piece of blank material, there is no need to reinforce the outer cylindrical portion with a separate member. Therefore, it becomes possible to provide a simple-constructed cylindrical member having a reduced number of component parts.
The cylindrical member may have a radically-extending wall portion that retains the plate thickness of the blank material. Therefore, since the radical wall portion of the cylindrical member, which does not receive so a high pressure in comparison with the outer cylindrical portion, is formed retaining the plate thickness of the blank, it is possible to provide a light-weight and rational cylindrical member not having any excess material.
The cylindrical member may be a front cover for a torque converter.
When the invention is applied to a front cover of a torque converter, the front cover, in which a higher hydraulic pressure acts on its outer cylindrical portion than on its radical sidewall portion, can be formed from a single piece of blank material, together with spline grooves. Therefore, it becomes possible to provide a simply-constructed front cover having a reduced number of component parts.
The cylindrical member of the invention may be a front cover of a torque converter in which the spline groove has a stepped portion adjacent its distal end, with a greater groove depth toward the distal end (the right side in FIG. 2), and in which a snap ring engagement groove is formed in that stepped portion.
Therefore, the stepped portion formed in the spline groove increases the depth of the spline groove, so that a fluid passage can be secured between the outer peripheral edge of a snap ring, fitted into the snap ring engagement groove, and the spline groove bottom. Therefore, circulation of a lubricating fluid can be promoted, and a highly reliable construction can be achieved.
Furthermore, in the invention, the outer cylindrical portion may be formed so that the wall thickness at the groove bottom is substantially equal to or greater than the wall thickness of the blank. Therefore, after a wall thickness greater than the thickness of the blank material is formed by the thickness-increasing roller, the spline groove can be formed by the forming roller so as to provide a wall thickness at the bottom of the groove substantially equal to or greater than the wall thickness of the blank. Therefore, the cylindrical member can sufficiently withstand the high pressure that acts thereon in use as a torque converter front cover.